This invention relates to the field of metal refining. More particularly, this invention relates to a safety device for protecting the covers of vessels in which crude iron or molten steel undergo metallurgical processes or alloying operations.
During the conventional refining of iron into steel, crude iron or molten steel will typically undergo purifying treatments or alloying processes. Typical purifying processes include, for example, reducing the sulfur content of iron for specialty steels. It is well known that both the blast furnace and the oxygen top blowing converter offer only limited desulfurization capabilities. As a result, the production of certain grades of steel necessitate the desulfurization of the crude iron or steel to be conducted outside the blast furnace or converter. Moveover, in a large number of metallurgical processes, other substances, such as alloying elements have to be introduced into the liquid metal melt. Accordingly, special containers or vessels known as ladles are used in both the above mentioned purifying treatments and alloying processes.
Commonly, the metallurgical vessels or ladles are provided with covers during the above discussed refining treatments. The use of a cover is quite advantageous as it reduces any undesirable interaction between the metal bath and the atmosphere, thereby reducing possible reactions between the oxygen or nitrogen in the atmosphere with the metal melt. Often, a suction device for removing waste gases is mounted over the vessels or ladles. These suction devices will also aid in preventing any air which has entered the vessel from contacting the melt. The cover is also important in order to prevent the metal melt from escaping and splashing during the refining treatments.
The shape of the cover will be adapted to the particular configuration of the ladle which is being utilized. These large and heavy covers are usually deposited on the ladle by means of a chassis having a hoisting unit. A conventional cover is often provided with plural apertures having entrances for introducing blowing lances, probes or filling wires into the interior of the ladle. The apertures will also allow waste gases to escape in a controlled manner.
Unfortunately, certain problems and deficiencies have developed with conventional commercial ladle covers. For example, while the cover initially rests firmly on the upper surface of the ladle, over the course of time, the supposed tight fit will become extremely porous due, in part, to the highly corrosive nature of the splashing metal and frothy slag. This porosity results from gaps which develop between the casing of the ladle and the ring of the ladle cover. These porous gaps adversely affect the necessary and important separation between the metal bath and the atmosphere (which the cover is intended to effectively provide). Moreover, the difficult operation of removing the splashed and/or frothed hot impurities from the ring of the cover and from the edge of the ladle is complicated and dangerous.
One attempt to overcome the above discussed problems is disclosed in Belgian Pat. No. 887,984 wherein the vessels or ladles are provided wih a hood having an open ended pipe attached to the center thereof which catches the splashed melt before it can contact the hood. This funnel-shaped hood is connected to a suction system. The hood is positioned over the casing of the ladle such that an annular spacing is provided between the hood and the edge of the ladle or vessel. The lower portion of the pipe is comprised of a refractory material and can be immersed into the bath if so desired. The pipe covers 60-80% of the free surface of the melt. The upper portion of the pipe is attached to the hood via plural intermediate members.
The hood type cover as described in the British patent suffers from certain drawbacks. For example, since the tubular shaped pipe is subjected to considerable temperature differences, it will undergo relatively large expansions and contractions which will lead to metal deformation and consequently, shorter service life and higher labor and replacement costs. Unfortunately, even if only small portions of the pipe are damaged, the entire pipe must be removed and replaced. Finally, prior to replacing a damaged pipe, the hood and suction system will perform inadequately thereby adversely effecting deoxidation and promoting undesirable "nitrogen pick up" in the metal bath.